Array antenna utilizing a plurality of active semiconductor elements



Aug. 11, 1970 n. A; FLERIETAL 3,524,136

ARRAY ANTENNA UTILIZING A PLURALITY OF ACTIVE SEMICNDUCTOR ELEMENTS /N vE/v 7012s.

DOMINIC A. FLERI ROBERT JA SOCCI Aug. 1l, 1970 D. A. FLt-:Rl ETAL ARRAY ANTENNA `U'IILIZING A PLURALITY OF ACTIVE SEMICONDUCTOR ELEMENTS 2 Sheets-Sheet 2 Filed July 16. 1968 RELATIVE PHASE SHIFT (degrees) F ig. 3.

REVERSE BIAS CURRENT (milliumperes) DOMINIC A. FLERI ROBERT J. SOCCI A TURA/Ex United States Patent O 3 524 186 ARRAY ANIENNA iJTrLlzlNG A PLURALITY F ACTIVE SEMICONDUCTOR ELEMENTS Dominic A. Fieri, Malba, and Robert J. Socci, Yonkers,

NX., assignors to General Telephone & Electronics Laboratories Incorporated, a corporation of Delaware Filed July 16, 1968, Ser. No. 745,231 Int. Cl. H01q 3/26; H03b 7/06; H04b 7/04 U.S. Cl. 343-100 12 Claims ABSTRACT OF THE DISCLOSURE An array antenna is described wherein the individual radiating elements are each coupled to a corresponding avalanche oscillator. Each oscillator contains an avalanche diode which exhibits a negative resistance upon the application of a DC bias signal. The individual oscillators are locked in frequency by the injection of a signal from a master oscillator. The relative phase of the oscillations of the frequency locked oscillators is varied fby changing the magnitudes of the applied DC bias signals. The variation in relative phase permits the beam of radiation emitted by the array antenna to be steered.

BACKGROUND OF THE INVENTION This invention relates to an array antenna utilizing s plurality of oscillators containing active semiconductor elements wherein the relative phase shift between oscillators is provided by controlling the magnitude of the DG bias signals applied thereto.

Generally, an antenna containing a collection of radiating elements and associated signal generating means is referred to as an array antenna. The use of multiple discrete sources of radiation is recognized as providing increased freedom in antenna design and enhanced control of the antenna radiation pattern when compared with the single continuous source type of antenna. In the design of array antennas, the circuitry connecting the radiating elements to the microwave source is provided with phase| variable components so that a time-varying radiation pattern can be generated. For example, the incorporation of an individual phase shifter in the supply circuit at a point between the corresponding radiating element and the microwave source permits the relative phase of the radiation from the element to be independently controlled. Consequently, if the amplitudes of the signals supplied to the radiating elements are maintained essentially constant and the relative phases thereof varied, the beam of radiation from the antenna can be steered without bulk physical motion of the antenna structure. This type of antenna is often referred to as a phased array.

In the initial development of phased arrays, low-inertia mechanical phase Shifters were utilized to provide the rapid scanning of the antenna pattern. These relatively slow mechanical elements were replaced by electronic phase shifters which provided inertia-less or electronic scanning and enabled beams to be pointed in a random manner over relatively wide angles in intervals of the order of a microsecond. The electronic scanning flexibility of phased arrays has Ibeen utilized in radar applications to achieve increased performance in the estimation of range and azimuth parameters.

The term array includes antenna systems employing hundreds or thousands of radiating elements and the associated electronic components. The radiation emitted by an array is normally in the microwave frequency range wherein waveguide is utilized to conduct the generated signal to the radiating elements. As a result, the size and complexity of the signal distribution networks cupled between the signal generator and the radiating elements 3,524,186 Patented Aug. 11, 1970 are among the limiting factors in considering the number of radiating elements to be incorporated in a particular array. Since the beam steering operation of the array relies upon the provision of relative phase differences between the signals at the radiating elements, an individual phase shifting element is required to be included in the microwave conducting path of each radiating element.

Generally, two types of phase shifting elements are utilized in phased arrays. One type employs a ferrite element positioned in a section of waveguide and is characterized by relatively slow changes in the amount of phase shift provided. Consequently, the ferrite phase shifter is utilized in relatively slow scanning phased arrays. The other type of phase shifter employs semiconductor diodes mounted within a section of waveguide and is utilized in fast scanning phased arrays. While these phase Shifters have been successfully employed in phased arrays, the requirement of at individual phase shifting element for each radiating element greatly increases the cost and complexity of the microwave signal distribution network needed to supply the phased signals to the radiators.

Accordingly, the present invention is directed to the provision of a phased array wherein each radiating element is provided with an individual oscillator utilizing an active semiconductor element. The individual oscillators are locked to a single frequency and the relative phase of an oscillator output signal is varied by changing the magnitude of a DC signal applied thereto. Since the oscillators are responsive to DC signals, the need for complex high power waveguide distribution networks is obviated. In addition, the individual phase shifting elements heretofore characteristics of phased arrays are no longer necessary SUMMARY OF THE INVENTION A phased array constructed in accordance with the present invention includes a plurality of radiating elements positioned to form a spaced array. An oscillator characterized by the fact that it employs an active semiconductor element to generate high frequency signals is coupled to each radiating element. The active element includes first and second electrodes and is responsive to the application of a DC bias signal applied therebetween. Typical active elements which are suitable for use in the present invention are the avalanche diode and the Gunnelfect device,

In addition to the plurality of radiating elements and the corresponding oscillators, the array includes means for applying a DC bias signal between the lirst and second electrodes of the active elements of the oscillators. The DC bias signal causes the oscillators to generate microwave signals which are supplied to the corresponding radiating elements. To insure that the oscillators generate signals at a single frequency, a master oscillator is provided. The master oscillator is coupled to each of the individual oscillators and maintains the output frequency of the individual oscillators essentially constant by the injection of the master signal into the oscillator circuit.

Thus, the oscillators are frequency locked so that the radiated energy is at a single master frequency. To obtain the relative phase shift of the output signals from the individual oscillators that is necessary for steering the beam emitted by the phased array, means for varying the magnitude of the DC bias signals applied to the individual oscillators is included in the system. The variation of the magnitude of the DC bias of a frequency locked oscillator utilizing a semiconductor active element is found to provide a relative phase shift of the output signal without substantially changing the magnitude of the output signal. Therefore, the relative phase shifts required for beam steering are obtained by varying the DC bias level at each oscillator. As a result, a phased array is provided without utilizing an individual phase shift element for each combination of oscillator and radiating element in the array.

In one embodiment of the invention, the radiating elements are each coupled to a corresponding avalanche oscillator. The avalanche oscillator comprises an avalanche diode mounted in a circuit configuration which is tuned at the frequency of oscillation of the diode. The diode has rSt and second electrodes and the application of a reverse-bias DC signal therebetween causes the diode to breakdown and exhibit a negative resistance. In cornbination with the tuned circuit, the application of a DC bias current results in the generation of a microwave signal, typically in the 8-12 gHz. frequency range.

The individual avalanche oscillators are frequency locked to a single frequency by providing an RF coupling path between the tuned circuit and a master oscillator. When frequency locked, the relative phase of an avalanche oscillator is found to vary substantially with a relatively small variation in the DC bias current. The change in relative phase takes place without a substantial change in the oscillator output power.

Further features and advantages of the invention will become more readily apparent from the following detailed description of specific embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a block schematic diagram of a phased array constructed in accordance with the invention.

FIG. 2 is a side-view in section of an element of one embodiment of the invention.

FIG. 3 is a curve showing the variation in relative phase shift with bias current for the embodiment of FIG. 2.

FIG. 4 is an exploded view of an element of a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a phased array is shown comprising a plurality of oscillators N1, N2, N3 Ny Each oscillator is coupled to a corresponding radiator n1, n2, et seq. The radiators are shown positioned to form a spaced array. In addition, each oscillator is coupled via a corresponding variable impedance element 14, et seq. t a bias source 11.

The oscillators are characterized by the fact that each contains an active semiconductor element, such as an avalanche diode or Gunn-effect device, which is caused t0 generate a signal in the microwave frequency range upon the application of a DC bias signal thereto. The variable impedance elements are provided in order to enable the magnitude of the bias signal applied to each oscillator to be varied independently. Since oscillators employing semiconductive active elements have a frequency of oscillation which is determined in part by the physical characteristics of the active element and in part by the tuned circuit or cavity in which the element is contained, the individual oscillators may have slightly different unlocked or free-running frequencies. To provide a single output frequency for all elements of the array, master oscillator 12 is coupled to each of the individual oscillators N1, N2, N3, et seq.

The injection of a signal from the master oscillator into each individual oscillator results in the frequency locking of the individual oscillators to the frequency of the master oscillator. Thus, the master oscillator controls the frequency of the beam of radiation emanating from the plurality of radiators n1, n2, n3, et seq. The beam of radiation is steered by varying the relative phase of the signal generated by each individual oscillator. In order to enable the beam to sweep in space, it is necessary to vary the relative phase of the signal generated by each oscillator independently of the phase variation in other oscillators. This independent variation is provided in the present array by varying the magnitude of the DC bias signal supplied to the individual oscillators. The variation in phase is obtained by including the Variable impedance elements between the bias source 11 and the oscillators. While these elements 14 et seg. are shown as potentiometers, it will be recognized that many different means for independently varying the level of the DC bias signal may be employed.

The construction of an individual oscillator N1 and its corresponding radiating element are shown in FIG. 2. The oscillator is an avalanche oscillator, so termed because the active element utilized in the generation of the oscillations is an avalanche diode. The avalanche diode is contained in a conventional microwave dio-de package 22 and is positioned within a section of waveguide 23. The electrodes of the avalanche diode are coupled to the opposite ends of the package. One end of the package is connected to a waveguide wall by extending into a mated recess in threaded conductive plug 25. The threaded plug extends into an opening in the waveguide wall and is held in place by threaded sleeve 24. The sleeve is secured to the external surface of the waveguide by solder to insure good electrical contact therebetween. Consequently, the electrode at this end of the package is maintained at a reference potential.

A coaxial connector 30 is attached to the opposing wall of the waveguide, for example by solder. An opening in the waveguide wall is centrally located at the base of the connector to permit external electrical connection to the diode package 22. The connector 30 contains a conventional coaxial connection and, in addition, provides a capacitive bypass for microwave energy propagating in the waveguide. The provision of a capacitive bypass at an opening in the wall of a waveguide insures that the opening appears as a short-circuit to the waves therein and, thus, has no significant effect on the transmission characteristics, e.g. leakage, of the waveguide. The capacitive bypass of connector 30 includes insulating washer 31, conductive disc 33 having an insulating sleeve 32 interposed between its outer surface and the inner surface of connector 30, and the center conductor 34.

As shown, center conductor 34 extends through the opening in the waveguide wall and engages the corresponding end of the diode package 22. The center conductor 34 is biased by spring member 35 into firm contact with the diode package. The opposing end of the spring member is attached to conductive plate 36 which is fastened to an electrically conductive tubular element 37. Element 37 is adapted to receive the center conductor of a mating external coaxial connector (not shown) and is insulated from its outer conductor 38 by insulating sleeve 39. The outer conductor 38 is designed to engage the outer conductor of the external coaxial connector.

To permit avalanche diodes to be interchanged or replaced with other types of active semiconductor elements, the outer conductor 38 is mounted on removable end plate 40 of connector 30. Also, the connector contains a removable insulating sleeve 41 to reduce the possibility of electrical contact occurring between the spring member 35 and the wall of connector 30. While a particular type of external connection has been described, it will be recognized that other types of external connections may be utilized if desired.

Waveguide 23 is provided with a flange 42 at one end which is shown coupled to a mating flange 43 of radiating horn 44. At the other end of the waveguide, tuning means 45 is provided. The tuning means, in the embodiment shown, comprises a sliding end wall of conventional construction. This end wall enables the impedance at the transverse plane of the waveguide containing the diode to be readily adjusted. Also, coupling means 46, which is a capacitive probe in this embodiment, is located in the wall of the waveguide for injecting the signal from the master oscillator 12 of FIG. 1 into the waveguide to provide the required frequency locking.

In operation, a plurality of the combined oscillator and radiating elements of FIG. 1 are mounted in a rack (not shown) to form a spaced array. The individual coupling means 46 are connected to the master oscillator. In addition, the connector 30 is coupled to a DC bias source which, in the case of an avalanche diode, supplies the reverse current which causes the p-n junction in the diode to break down and a negative resistance characteristic to be exhibited by the diode. Typically, the DC voltage required to supply the reverse current needed to promote an avalanche breakdown is of the order of 40 volts.

When the diode is heavily reverse-biased, a resonant condition at the frequency of oscillation of the diode is obtained at the transverse plane containing the diode. The condition is reached when the net reactive impedance at this plane is essentially zero. In the embodiment shown, the tuning effect is provided by varying the position of the sliding shorted end wall. However, other types of tuning means may be utilized if desired. When the resonant condition is obtained, the diode is, in effect, a generator of high frequency energy. The energy is supplied to the radiating horn and is emitted therefrom.

Since the characteristic frequency of oscillation of the diodes in the array may be different and it is desired to provide an array which emits radiation of a single frequency, the frequency of oscillation of the individual diodes is locked to a single frequency by injection locking. The technique of injection locking utilizes the fact that the frequency of an oscillator circuit can be varied and locked to that of an injected signal provided that the free-running individual oscillator frequency is relatively close to the master frequency. The frequency range over which injection locking can be utilized is determined primarily by the Q of the tuned circuit and the power output levels of both the individual and master oscillators. The relationship controlling injection locking are set forth in greater detail in an article entitled A Study of Locking Phenomena in Oscillators by R. Adler appearing in Proc. of IRE, June 1946 at p. 351. Thus, coupling each individual oscillator to a master oscillator insures that the energy from each radiating element is at the master frequency.

The capability of a phased array to provide a steered beam of radiation requires that the relative phase of the energy being emitted from each radiating element be independently controlled. It has been found that the phase of the microwave signal generated by an oscillator in the present array can Ibe readily varied by changing the level of the DC bias signal applied thereto. Thus, the potentiometers of FIG. 1 provide the phase control of the array. In one embodiment tested and operated with oscillators utilizing Sylvania D5540 gallium arsenide avalanche diodes, the oscillators were locked to a frequency of approximately 8.9 gHz. The relative phase shift in degrees between the oscillator signals for different levels of reverse bias current is shown in FIG. 3. As shown, a variation of 1.5 milliamperes between bias levels provided about 100 degrees in phase shift. The variation in emitted power observed for this phase shift was of the order of 1.2 db. In this embodiment, the power level of the locking signal from the master oscillator was approx.- imately db below the output power level of an indi- Nidual oscillator. However, it will be recognized that the power of the locking signal depends primarily on the frequency separation between the master oscillator and the individual oscillators, the output power of the avalanche oscillators and the electrical characteristics of the circuit.

A second embodiment of the invention is shown in FIG. 4 wherein an individual oscillator and a corresponding dipole radiating element are formed in a microwavetype of integrated circuit. This type of construction enables the density of the phased array to be substantially increased since the physical size and complexity of an oscillator and associated radiating element are reduced when compared with the embodiment of FIG. 2.

The embodiment of FIG. 4 utilizes rst and second dielectric layers 51 and 52 with the oscillator formed. therebetween. The structure is shown in an exploded perspective view with the oscillator Ni comprising an avalanche diode 53 connected in series with center con ductor 54. The rst and second electrodes of the diode are coupled to first and secondbias terminals 57 and 53 through low-pass filters 55 and 56 respectively. A capacitive gap 59 is shown in center conductor 54 and provides DC isolation between the radiating element and the oscillator. The avalanche diode `53 is shown as a chip type structure with its first and second electrodes on the upper and lower surfaces thereof. Although the diode is connected in series with center conductor 54, a shunt connection may be employed if desired. 11n this type of connection, one electrode of the diode is coupled to center conductor 54 and the other electrode is coupled to a ground plane which is at a reference potential.

As shown, the center conductor `54 extends beyond the gap 59 toward the edge of layer 51. This portion of the center conductor in combination with extensions 61 and '62 of the rst and second ground planes 71 and 72 formed on the outer surfaces of layers 51 and 52 respectively constitutes a dipole radiating element. The right angle extensions 63 and 64 have a length of one-quarter wavelength at the frequency of interest. In addition, a shorting bar 65 is contained within layer 51 and is electrically connected to center conductor 54 and ground plane conductor 71.

The application of the reverse bias DC signal between terminals 57 and 58 causes the diode to experience reverse breakdown and exhibit a negative resistance. The length of the portion of center conductor 54 which extends from the diode in the direction away from the radiating element is selected so that its reactance establishes a tuned circuit for the diode. The combination of the diode and the reactive length of center conductor 54 form an oscillator which provides microwave energy at the characteristic frequency of the diode and circuit. To lock the frequency of oscillation to the master frequency, the signal from the master oscillator (not shown) is coupled into the tuned circuit via conductor 66. As shown, conductor 66 is provided with an external terminal 69 and an L-shaped extension 67. A deposit of lossy material 68 is located at the end of extension 67 to form a non-reilecting termination. The major portion of extension 67 is proximate to the center conductor 54 of the oscillator so that the signal travelling on the transmission line comprising center conductor 66 and ground planes 71 and 72 is capacitively coupled to center conductor 54. As a result, the master oscillator signal is injected into the diode tuned circuit and frequency locking takes place.

Although the embodiment of FIG. 4 utilizes a strip transmission line as contrasted with the waveguide structure of the embodiment of FIG. 2, the operation of the oscillator and corresponding radiating element are similar. The application of the DC bias signal between terminals 57 and 58 causes the oscillator to generate the high frequency signal which is emitted by the associated radiating element. The frequency of these signals is locked by the coupling of the master oscillator to the tuned diode circuit. A variation in the level of the applied DC bias signal changes the phase of the emitted signal as described in connection with the embodiment of FIG. 2. In practice, a plurality of oscillator-radiating element components may be formed on common dielectric layers to thereby reduce the size and complexity of a phased array utilizing a large number of individual sources.

While the above description has referred to specific embodiments of the invention, it will be apparent that many variations and modifications may be made therein.

What is claimed is:

1. An array antenna for generating a variable radiation pattern which comprises:

(a) a plurality of oscillators, each of said oscillators containing an active semiconductor element having first and second electrodes, said oscillators being characterized by the fact that they generate high frequency signals upon the application of a DC bias signal between the first and second electrodes of said active elements;

(b) a plurality of radiating7 elements positioned to form a spaced array, each of said radiating elements being coupled to a corresponding oscillator;

(c) means for locking the frequency of said plurality of oscillators to a single frequency;

(d) means for applying a DC bias signal between the iirst and second electrodes of each of said active elements whereby said oscillators generate the high frequency signals to `be radiated; and

(e) means for varying the level of the DC bias signal applied to each active element and thereby changing relative phase of the radiation emitted by the individual oscillators varying the radiation pattern emitted by the array antenna.

2. The array antenna in accordance with claim 1 wherein each of said oscillators additionally comprises a tuned circuit including said active element, said circuit being tuned to resonance at the frequency of oscillation of said active element.

3. The array antenna in accordance with claim 2 wherein said active elements are avalanche diodes.

4. The array antenna in accordance with claim 3 wherein said oscillators each contain means for tuning the circuit containing the avalanche diode.

5. The array antenna in accordance with claim 2 wherein said active elements are Gunn-effect devices.

6. The array antenna in accordance with claim 2 wherein each of said oscillators further comprises a section of waveguide containing the active element therein and means for tuning said waveguide to resonance at the transverse plane containing the active element, said waveguide being coupled to the corresponding radiating element.

7. The array antenna in accordance with claim 2 wherein each of said oscillators further comprises:

(a) rst and second dielectric layers, the outer surfaces of said dielectric layers containing ground planes;

(b) a center conductor formed on the inner surface of said first dielectric layer;

(c) an active semiconductor element having iirst and second electrodes, at least one of said electrodes being coupled to the center conductor;

(d) means for applying a DC bias signal between the first and second electrodes of said active element; and

(e) a radiating element electrically coupled to said center conductor.

S. The array antenna in accordance with claim 7 wherein said active element is mounted in series with said center conductor.

9. The method of varying the relative phase of two microwave oscillators each of which contains an active semiconductor element, said oscillators being characterized by the fact that they generate high frequency signals upon the application of DC bias signals to said active elements, comprising the steps of:

(a) frequency locking said oscillators so that they generate said high frequency signals at the same frequency, and

(b) varying the DC bias signal applied to one of said active elements.

10. The phase varying method as deiined Iby claim 9 wherein said frequency locking is accomplished by injection locking.

11. The phase varying method as dened by claim 10 wherein said semiconductor elements are avalanche diodes.

12. The phase varying method as defined by claim 10 wherein said semiconductor elements are Gunn-elect devices.

References Cited UNITED STATES PATENTS 7/1968 Warner 331-107 2/1969 Aasted et al.

U.S. Cl. X.R. 331-107; 343-854 

